Adaptec 2400A Performance

[Rishi Chopra]

Just wanted to make sure I wasn't skipping any obvious steps.

One other (slightly lamer) question: if my device configures as da0, is 
that scsi or ide?

The reason I ask is I wish to write a custom kernel, and would like to 
eliminate all unnecessary configurations/devices.

Charles Swiger wrote:

> On Jan 24, 2004, at 12:51 AM, Rishi Chopra wrote:
> 
>> I was rather disappointed with the results.  Can anyone suggest what 
>> might be causing such slow disk speeds, or whether these speeds are 
>> out of the ordinary for a 4-disk FreeBSD RAID5 installation?  I have 
>> done nothing to configure the card aside from striping the array in 
>> BIOS; FreeBSD seems to automatically detect the disks.
> 
> 
> For us to be able to comment beyond generalizations, it's necessary to 
> also benchmark how a single disk performs.  I can still answer your 
> question, though:
> 
> RAID-5 is slow.  RAID-5 trades availability against performance and 
> hardware costs.  With RAID-0, n drives gives n drives' worth of usable 
> space.  With RAID-5, n drives gives n-1 drives' worth of usable space.  
> The performance is between RAID-0 and RAID-1 is comparible for large 
> accesses.  For small accesses, particularly small writes, RAID-5 
> performance is much worse than plain RAID-0 or a plain disk.
> 

-- 
Rishi Chopra
http://www.ocf.berkeley.edu/~rchopra